The realization of receiver systems operating with wide instantaneous bandwidth and tolerant to strong in-band blockers has been a long-standing challenge faced by CMOS circuit designers. Research has focused on developing circuit topologies that are able to mimic the rejection properties of off-chip filters. These approaches include n-path filters, mixer-first receiver architectures, filtering by aliasing, and compressive sensing based receivers, to name a few. One limitation of these techniques has been the inability to support large instantaneous fractional bandwidths.
The ideal receiver for future wireless communication systems will collect a very wide swath of spectrum and adaptively choose which parts of it to extract. In addition, as a result of the intense demand for spectrum for commercial uses, there is a decrease in the available spectrum for measurements that require extreme quiet such as remote sensing of the earth and radio astronomy. In these modern communications and remote sensing applications, the systems are interference-limited, and thus a significant issue for a receiver that covers a very wide bandwidth is that the RF input stages need to process spectra having very weak signals from a distant source mixed in with strong signals from nearby sources. Practical nonlinearities in current receivers make the separation of such signals a key barrier to the realization of these dynamic spectrum access systems. In order to remain adaptable, current receivers typically avoid fixed filters at their input and immediately use a low noise amplifier or active mixers to raise the signal level above the noise introduced by subsequent digital filtering. However, this approach introduces nonlinearity at the point where the as yet unfiltered interferers are large enough to cause distortion that can mask weaker signals. Therefore, there is a need for a receiver that mitigates the challenges imposed by these nonlinear components, hence greatly improving receivers that can process very wide bandwidths where interference is normally a critical limitation.